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Most code I write is in PHP. I have recently started learning shell scripting. Most of the resources and tutorials that I've come across are specific to Bash. Some warn about bashisms and some don't. I've been reading a lot on here and Stack Overflow.

Whenever an answer uses bashisms, someone will inevitably comment to say:

You shouldn't use <insert bashism here>. It's not portable.

This happens even when the question was tagged with bash. To me, that's like telling a PHP programmer that they shouldn't use code that's new in PHP 5 because it can't be used with PHP 4. Or telling someone they shouldn't write something for Mac because it can't be used on Windows.

When I write in PHP, I pick a minimum requirement and I write forward-compatible code. I don't worry about making it backward-compatible.

If I use #!/bin/bash as the shebang, why shouldn't I use bashisms? I'm starting to get the impression that some people just like to bash bashisms (pun intended) just for the sake of it.

People often use bash and shell interchangeably - probably due to the fact that bash is the default shell on many systems. So I can understand adding a comment to warn that the code uses bashisms, but I don't understand the implication that it's wrong to use them.

Obviously, if I am writing a script strictly for personal use I can write it in whatever language I want. But I'd like to think some of the code I write could be useful to others.

I tried searching for an answer to my question before posting. I found a lot of information about how to test for portability, but couldn't find anything about when it's important to do so.

So, when is it important to write portable scripts?

For example,

  • what types of scripts should be as portable as possible?
  • how common are systems that do not have Bash installed?
  • if the system has Bash installed, will it also have the GNU version of find and other utilities?
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    I upvoted this question and answered it, but the more I think about it only the last 2 questions fit with the site. The others a "primarily opinion based". Commented Mar 14, 2014 at 6:12
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    There is also a meta aspect in this question: While it may not help the initial answering of the question, comments like "this is not portable" can be very helpful for other readers stumbling accross the question/answer months or years later. Commented Mar 14, 2014 at 10:02
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    @Bananguin Comments saying "this is not portable" don't bother me. That's just an FYI. I've made those types of comments myself. It's the "You shouldn't use..." that bothers me. It implies that there is something wrong with the answer. That would be valid if the answer was recommending deprecated code, for example. So it had me wondering what is wrong with Bash. Commented Mar 14, 2014 at 10:52
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    +1. Especially when the question has bash tag alone, someone comments "It's bashism and not portable". When I answer a question that's tagged C, I don't care whether it's portable to Java or not. Commented Jul 23, 2014 at 14:43
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    I feel it's always good to point about that it's a bash specific feature, and not portable, just as I would point out that a GNU specific extension is being used for some utility (even though the question was tagged as Linux). I've never seen anyone say "this is a bashism and you should never use it". Commented Jan 16, 2015 at 17:57

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As a member of this community I do not often see people disregarding bashisms for things that target bash. When talking about portability, GNUisms are much worse than bashisms. As long as you use bash for your shebang, you can expect the script to be executed using bash. However, you can't guarantee the version unless you explicitly check. Bash version 4 brought some useful features such as associative arrays, but Bash v3 is still widely used on OS X and RHEL 5.

what types of scripts should be as portable as possible?

This is more about your needs and what you choose to support as the developer. If you are writing an install script for an application that supports all types of *NIX, then portability will be very important.

how common are systems that do not have Bash installed?

FreeBSD and Solaris 10 are examples of systems that do not come with bash installed by default. Most Linux systems will have it, with the exception of embedded systems.

if the system has Bash installed, will it also have the GNU version of find and other utilities?

No, and this is the real issue with portability. If portability is important, you should only use shell command features that are defined by the POSIX standard. GNU utilities can be installed on non-GNU systems such as FreeBSD, but they are unlikely to be first in PATH, and you can not rely on those tools to be installed.

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    I think it's more on SO than here where I often see people disregarding bashisms. I just know that I've noticed it often enough to frustrate me and prompt me to ask this question. Commented Mar 14, 2014 at 6:20
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    So if GNU utilities are installed but not first in PATH, is there a way to call them specifically? Otherwise, why have them installed at all? Commented Mar 14, 2014 at 6:22
  • @toxalot: Binaries and scripts are called explicitly by using absolute paths. Commented Mar 14, 2014 at 10:05
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    @Bananguin So if someone had Bash and GNU utilities installed (but not in PATH), they could use the script if they edit it to use absolute paths for find and whatever other GNU-specific utilities I had used? Obviously, that would not be user-friendly for an installer script. But I'm thinking of just putting something on GitHub for others to grab if they so desire. I don't care that it's not portable to every system. I just don't want it to be useless on many systems. Commented Mar 14, 2014 at 11:15
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    @toxalot: yes that could work. if you put something like FIND=/opt/gnu/dispicable/bin/find at the beginning of your script and then use ${FIND} instead of find in your script you give people one (!) place to put their install paths and make your script use the correct tools. Commented Mar 14, 2014 at 12:27
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So, when is it important to write portable scripts?

what types of scripts should be as portable as possible?

When you're using them for your working environment, and you work (or could in the future) on different machines - AND, you don't want to have to rewrite your tools prior to getting down to work.

eg: a trash script / rm replacement

Mark Stewart:

...for my troubleshooting toolkit I assume I will only have vi and Korn shell. And I try to use commands that work on most flavors of Unix.

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    I like some of the slick "Bash-isms" but for my troubleshooting toolkit I assume I will only have vi and Korn shell. And I try to use commands that work on most flavors of Unix. That way I'm ready to do triage on a sick system without having to worry about how the ps command behaves, whether Bash or Perl or PHP is there, or where they are. Commented Jan 16, 2015 at 17:04

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